Single-mode lasing by selective mode pairing

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Science  08 Feb 2019:
Vol. 363, Issue 6427, pp. 586-587
DOI: 10.1126/science.aaw1203

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Many laser applications require compact integrated laser sources combined with single-mode, high–output power operation. This task is often daunting, given the presence of optical nonlinearities and thermal effects. A standard approach to address nonlinear-induced complications, like beam filamentation, is to use array architectures of evanescently coupled single-mode gain photonic cavities. Unfortunately, these arrays support multiple lasing modes (“supermodes”) that spoil the quality of the emitted beam (1). One way to address this problem is through selective amplification of only one mode, typically the fundamental (2). On page 623 of this issue, Hokmabadi et al. (3) take a different approach based on an earlier theoretical proposal by El-Ganainy et al. (4). They promoted the lasing of the fundamental mode by suppressing the undesired higher-order modes through judicious “pairing” with a set of low–quality factor Q modes. The pairing occurred by using strategies inspired by supersymmetry (SUSY). Specifically, these lossy superpartners are supported in a SUSY-engineered adjunct array in such a way that they are phase-matched with the unwanted highorder modes of the lasing array.